Process for the treatment of lead ores



before being charged United States Patent 2,823,990 PROCESS FOR THE TREATMENT OF LEAD ORES Josef Barwasser, Udo Esch, Werner Schwartz, and Hans Rausch, Frankfurt am Main, Germany, assignors to Metallgesellschaft Aktiengesellschaft, Frankfurt am Main, Germany No Drawing. Application April 29, 1954 Serial No. 426,576

Claims priority, application Germany April 30, 1953 6 Claims. (Cl. 75-77) The present invention relates to an improved process for smelting sulfidic lead ores or concentrates thereof and particularly sulfidic lead containing materials which are rich in lead.

Lead ores are as a rule smelted in shaft furnaces, in such a manner that the furnace charge does not contain over 40% of lead as otherwise the gas permeability of the charge otters too great a resistance to the blast passing through the shaft furnace so that the reaction is slowed to too great an extent and sometimes stops entirely. As the fine grained flotation concentrates which are available today have lead contents up to 80%, these are usually diluted by additions of slag and silicate or lime containing materials to a 40% lead content, and this diluted material was sintered to convert it to a coarsely granular form into the shaft furnace. Aside from the fact that it is not technically nice to reduce a previously attained high concentration and consequently reduce the space throughout as well as heat economy and furthermore greatly increase the quantity of slag produced, the necessary presintering requires additional apparatus with corresponding amortization and running costs.

This disadvantage can, in part, be avoided by decomposing rich lead ores or concentrates to'lead and sulfur dioxide by blowing in air on socalled Newnam hearths or Schlippenbach apparatus to etfect the known roasting reaction. Such processes however only directly lead to a maximum of 80% direct recovery of lead. The remaining lead content must be recovered in the manner indicated above with sintering apparatus and shaft furnaces.

While such processes do oifer certain advantages over smelting in shaft furnaces, it is not possible thereby to render use of shaft furnaces and sintering apparatus superfluous. Furthermore, in view of the rather ramified flow of the materiahthe labor costs involved are relatively high and dusting problems are substantial.

A further proposal has also been made for smelting rich lead ores or concentrates in which such ores are smelted together with soda, carbon and iron oxide in a stationary flame furnace at about 1000 to 1200 C. in order to bind the sulfur content of the ore by the soda and iron oxide. It has also been proposed to replace a portion of the soda with sodium chloride. This process renders it possible to smelt to richest lead ores or concentrates without the necessity of presintering, but on the other hand requires very considerable quantities of heat as the heat transfer within fine grained material at rest as it occurs exclusively in flame furnaces is, as is well known, extraordinarily poor.

Furthermore, the molten sulfide phase which is produced during the smelting contains considerable quantities of lead. The quantity of lead in the sulfide phase does decrease gradually by continuing the heating but it is not economical to continue the heating until the sulfide phase is completely de-leaded as the heat requirements would be too great and furthermore, at the high temperatures employed, the volatility of metallic lead and lead sulfide are such as to cause losses of lead values.

salts and also iron oxide can be At the end of such a process the sulfide phase primarily consists of Na s and FeS. These materials are capable of dissolving the gangue contained in the lead ore so that a relatively pure metallic lead results. However, separation of lead from its accompanying metals such as copper, arsenic and the like is not achieved in a single step.

it is the object of the present invention to provide a process whereby even the richest lead one concentrates can be smelted directly to metallic lead with simultaneous separation of the lead from its accompanying metals without necessitating use of sintering or gas cleaning apparatus.

it is a further object of the invention to provide a process having lower heat requirements than the previous known processes and having substantially no losses of lead by dusting or evaporation of metallic lead or lead sulfide.

The process according to the invention essentially consists in smelting the lead ore or concentrate together with soda and carbon in a rotating flame furnace at temperatures between 700-1000" C. If desired a portion of the soda can be replaced by sodium chloride or other sodium added to the charge.

The temperature employed depends upon the composi tion of the ore and is the higher, the greater its content in diflicultly melting gangue, but in every instance is considerably lower than in all the other smelting processes described above. As a general rule it may be said that the temperature required is roughly 200 C. lower than that required when the reaction is carried out in a stationary flame furnace. In view of the relatively lower temperatures required for the process according to the invention, evaporation of lead and lead sulfide is avoided to a large extent and as the good heat transfer effected in a comparatively short period of time, evaporation losses are not discernable in commercial operation of the process. However, the most important advantage of the process according to the invention is that the sulfide phase produced is practically free of lead sulfide right from the start, so that separate recovery of lead from this phase is not necessary, and substantially all of the lead contained in the charge is recovered directly as lead of high purity.

A further substantial advantage of the process according to the invention is that it permits separation of lead from a number of accompanying metals in one operational step. It was found unexpectedly that the soda only binds the sulfurbound to lead and not that bound to copper or arsenic. Consequently copper and arsenic go into the sulfide phase and a metallic lead free of these metals is obtained. Antimony and the noble metals on the other. hand remain with the lead and can be separated therefrom by the usual refining methods. Of course, if hard lead is desired it is not necessary to separate the antimony therefrom. The noble metals are not lost in the sulfide phase whose working up only pays when it contains large quantities of copper. Furthermore, the major proportion of bismuth present also goes into the sulfide phase so that, when not too high a bismuth content is originally present, lead with a permissible bismuth content can be obtained in one operational step. As is well known, bismuth is the most deleterious impurity of lead as it can only be removed with great ditficulty during refining.

A further 20% saving in heat costs can be achieved in the process according to the invention when the smelting is carried out in a short rotary flame furnace, that is, a flame furnace with a reverberatory flame, whose interior length is not substantially greater than its internal diameter, preferably one rotating about a horizontal axis.

In accordance with a further modification of the process according to the invention the time grained raw materials are granulated before they are charged into the 3 m. The charging took minutes.

'total lead content of the charged concentrate.

rotary furnace. It has been found advantageous to effect formation of the granules from the fine material wetted with hot water of about 50-70 C.

With granulation of the charge, it has been found that the time required for smelting a charge can be materially shortened as rotation of the furnace can commence directly after it has been charged so that the better heat transfer effected thereby can be utilized during the entire period rather than just a portion thereof. Furthermore,

the intimate mixture of the reaction components effected thereby also favorably affects the time required for the reaction, which in turn lowers the quantity of fuel re- ,quired by about 2030%. Furthermore, because of the .more favorable angle of slope of the granules, the time required for charging the furnace can be shortened and .dust losses are avoided. Also use of a granulated charge :effects a certain saving in chemicals, as the intimate mixture of the reaction components renders it possible completely to use up the added chemicals. As the dust losses are reduced to a non-detectable minimum during plant .operation, no losses of lead occur in the exhaust gas.

The mixture was :charged in a quantity of 3500 kgs. to

a rotary furnace with a diameter of 3 m. and a length of Hereafter the heat was turned on and after more minutes, i. e. minutes after begin of charging, the furnace was put into rotation. The temperature maintained in the furnace was 850 C. 160 minutes after begin of charging the heat- -ing and rotation was stopped and slag and molten metal was drawn. The recovery of lead was 99.4% of the The lead contained 99.6% Pb and 0.1% Cu, i. e. roughly of the copper content of the concentrate was contained in .the slag.

Example 2 The lead concentrate of Example 1 was granulated together with Percent Na CO 9.0 Iron oxide 17.0 Waste coal 4.9

on a gran'ulator by the aid of water of 60 C. The granules were charged to the furnace described in Example 1. The charging took 4 minutes. After completing of charging the flame was ignited and at the same time the furnace put into rotation. Treating temperature 850 C. minutes after begin of charging the treatment was terminated. The recovery of lead was 99.6%, purity of lead the same as in Example 1.

Example 3 The lead concentrate of Examples 1 and 2 was granulated together with Percent Na CO 7.2 NaCl 3.5 iron oxide 19 Coke breeze 5.3

Duration of charging and treatment was the same as in Example 2, treating temperature 900 C. The recovery of lead was 98.8% and the lead contained 99.6% Pb and 0.1% Cu.

We claim:

1. In process for smelting sulfidic raw materials containing more than 40% of lead in the form of lead sulfide in admixture with soda and carbon the steps which comprise granulating an admixture of a lead ore concentrate with soda and carbon wetted with water of a temperature of 50 to 70 C., and smelting the resulting granulated admixture in a flame-fired rotary furnace at a temperature between 700 and 1000 C.

2. The process as claimed in claim 1 in which said smelting operation is carried out in a short flame-fired rotary furnace whose inner length does not substantially exceed its inner diameter.

3. The process as claimed in claim 1 in which said smelting operation is carried out in a short horizontal References Cited in the file of this patent UNITED STATES PATENTS 821,330 Betts May 22, 1906 1,218,412 Kissock Mar. 6, 1917 1,844,428 Kohlmeyer Feb. 9, 1932 2,381,970 Collins Aug. 14, 1945 

1. IN PROCESS FOR SMELTING SULFIDIC RAW MATERIALS CONTAINING MORE THAN 40% OF LEAD IN THE FORM OF LEAD SULFIDE IN ADMIXTURE WITH SODA AND CARBON THE STEPS WHICH COMPRISE GRANULATING AN ADMIXTURE OF A LEAD ORE CONCENTRATE WITH SODA AND CARBON WETTED WITH WATER OF A TEMPERATURE OF 50 TO 70* C., AND SMELTING THE RESULTING GRANULATED ADMIXTURE IN A FLAME-FIRED ROTARY FURNACE AT A TEMPERATURE BETWEEN 700* AND 1000* C. 